Changed atan to atan2 for transfroming coordinates from cartesian to spheri...

Samo Penic

2014-04-17 e9c87efeb9235748e8d19a3f5a067ec442d8a500

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Original written by Dan Kroll in FORTRAN. Code was then largely adapted and commented by Miha Fosnaric-Fosni. Rewritten into C by Samo Penic-Peni, with help of Miha's extensive explanations.